Triassic cynodonts from South America are key taxa in the investigation of the emergence of mammalian characters. One of the most iconic species from the Carnian is Prozostrodon brasiliensis, found in Late Triassic strata from southern Brazil. This non-mammaliaform cynodont represents the earliest-diverging member of Prozostrodontia, a clade that encompasses Mammalia and their closest relatives. Previous descriptions of the skull of Pr. brasiliensis were based on specimens that did not preserve the posterior region, obscuring essential details of the basicranium. Here, we describe a new, complete, and exceptionally well-preserved skull of Pr. brasiliensis found in the same block as the holotype skeleton of the early predatory dinosaur Gnathovorax cabreirai and rhynchosaur specimens. Anatomical data from this specimen provide novel insights into the initial radiation of prozostrodontian cynodonts and reveal a new endemic clade of South American cynodonts – Prozostrodontidae – on the stem lineage of mammals.

来自南美洲的三叠纪犬齿兽类是研究哺乳动物特征出现的关键类群。卡尼期最具标志性的物种之一是Prozostrodon brasiliensis，它发现于巴西南部的晚三叠世地层。这种非哺乳类犬齿兽代表 Prozostrodontia 中最早分化的成员，Prozostrodontia 是一个包含哺乳类及其近亲的进化枝。Pr.头骨的先前描述。brasiliensis基于不保留后部区域的标本，掩盖了颅骨的基本细节。在这里，我们描述了一个新的、完整的、保存完好的Pr头骨。巴西人发现于与早期掠食性恐龙Gnathovorax cabreirai和犀龙标本的正模骨架相同的区块中。该标本的解剖学数据提供了对犬齿兽齿兽原始辐射的新见解，并揭示了南美洲犬齿兽类的一个新的地方性分支——Prozostrodontidae——在哺乳动物的茎谱系上。